1. Field of the Invention
The present invention relates to an aqueous colorant dispersion with good dispersibility of colorant, a method for producing an aqueous colorant dispersion, and an aqueous ink for inkjet recording.
2. Description of the Related Art
In recent years, with the increase in demands for resource protection, environmental protection, and higher safety during operations, demands for water-based paints and inks (hereinafter may be collectively referred to as “ink”) are increasing. Water-based paints and inks are, as is the case with oil-based paints and inks, required to have flowability, storage stability, glossiness of coatings, clarity, and coloring power. However, most pigments are not well dispersed in water-based vehicles in comparison with oil-based vehicles, and thus cannot provide satisfactory quality by an ordinary dispersion procedure. In order to solve this problem, the use of various additives such as dispersing resins for aqueous pigment dispersion and surfactants has been studied, but there is still no water-based paint or ink which satisfies all the above-described requirements and is comparable to known high quality oil-based paints or inks.
In order to solve the above problem, for example, an aqueous pigment ink containing a pigment dispersion capsulated with a polymer containing 20 to 70% by mass of aromatic rings is disclosed in, for example, U.S. Patent Publication No. 2005/0124726 A1.
In addition, a pigment ink for inkjet recording containing a pigment dispersion in which a random copolymer of a hydrophilic monomer and a hydrophobic monomer in an amount of 50 to 80% by weight with respect to the polymer weight is used as a dispersant is disclosed in, for example, U.S. Patent Publication No. 2006/0014855 A1.
However, in the U.S. Patent Publication No. 2005/0124726 A1, the content of the aromatic rings contained in the polymer for capsulating and dispersing the pigment is too high, so that the ink prepared by the technique disclosed therein cannot provide satisfactory properties of an aqueous ink, specifically redispersibility. In U.S. Patent Publication No. 2006/0014855 A1, the dispersant polymer is too hydrophilic, so that the ink prepared by the technique disclosed therein is too viscous, and insufficient in stability over time of the viscosity and dispersion particle diameter. In addition, when the aqueous inks prepared by the techniques disclosed in U.S. Patent Publication Nos. 2005/0124726 A1 and 2006/0014855 Al are used as inkjet recording inks, they cannot provide satisfactory ejection stability.